1. Field of the Invention
The present invention relates to a method for producing L-cysteine or related substances. More precisely, the present invention relates to a bacterium suitable for the production of L-cysteine or related substances and a method for producing L-cysteine or related substances utilizing such a bacterium. L-cysteine and L-cysteine-related substances are used in the fields of drugs, cosmetics, and foods.
2. Brief Description of the Related Art
Microorganisms which are able to produce L-cysteine are known, for example, a coryneform bacterium with increased intracellular serine acetyltransferase activity has been described (Japanese Patent Laid-open (Kokai) No. 2002-233384). Increasing L-cysteine-producing ability by incorporating a mutant serine acetyltransferase which is desensitized to feedback inhibition by L-cysteine has also been described (Japanese Patent Laid-open No. 11-155571, U.S. Patent Published Application No. 20050112731, U.S. Pat. No. 6,218,168).
Furthermore, microorganisms in which the ability to produce L-cysteine is enhanced by suppressing the L-cysteine decomposition system are also known, for example, coryneform bacteria or Escherichia bacteria have been reported in which the activity of cystathionine-β-lyase (U.S. Patent Published Application No. 20050112731), tryptophanase (Japanese Patent Laid-open No. 2003-169668), or O-acetylserine sulfhydrylase B (Japanese Patent Laid-open No. 2005-245311) is attenuated or deleted.
Furthermore, the ydeD gene, which encodes the YdeD protein, participates in secretion of the metabolic products of the cysteine pathway (Dabler et al., Mol. Microbiol., 36, 1101-1112 (2000)). Other techniques for enhancing L-cysteine-producing ability are known, including by increasing expression of the mar locus, emr locus, acr locus, cmr locus, mex gene, bmr gene, or qacA gene. These are all genes which encode proteins which function to secrete toxic substances out of cells (U.S. Pat. No. 5,972,663). The emrAB, emrKY, yojIH, acrEF, or cusA genes are also known (Japanese Patent Laid-open No. 2005-287333).
Furthermore, an L-cysteine-producing Escherichia coli has been reported in which the activity of the positive transcriptional control factor of the cysteine regulon encoded by the cysB gene is increased (International Patent Publication WO01/27307).
The d0191 gene is a novel gene of Pantoea ananatis which was found by the inventors of the present invention. Although presumably homologous genes to d0191 have been found in various bacteria by homology searches, the functions of all of them are unknown, and their relation with L-cysteine production is also unknown.